With a hybrid work vehicle in which a motor generator assists an internal combustion engine, the vehicle is caused to run with power supplied from the internal combustion engine, and the motor generator is operated as a motor in accordance with running conditions (vehicle speed, amount of operation of an accelerator pedal (accelerator opening), operation state of internal combustion engine, state of running road surface, gear position, remaining battery capacity, etc.), and the running of the vehicle is assisted with power that is output from the motor generator. Also, this motor generator can be operated as a generator, and can supply electricity to a battery to charge it. The vehicle is configured such that, when the motor generator is operated as a motor, torque (assistance torque) that should be borne by the motor generator can be generated in accordance with a ratio between vehicle drive torque to be borne by the internal combustion engine and vehicle drive torque to be borne by the motor generator with respect to the vehicle drive torque required by a driver (target vehicle drive torque, which is obtained based on an accelerator pedal operation by a driver etc., for example) (this load ratio is specified based on running conditions etc.), by controlling torque generated by the motor generator.
For example, with a hybrid power unit disclosed in Patent Literature 1 (JP 2002-252904 A), two control maps with different assistance patterns (relationships between the number of engine revolutions and torque) for an internal combustion engine by a motor generator are prepared, and the control maps are switched to perform assistance control in accordance with state information such as the state of battery charging capacity (SOC), the vehicle speed, the state of a transmission, and the internal combustion engine temperature. Thus, excellent driving performance is maintained while using a small-horsepower internal combustion engine.
Also, with a hybrid power unit disclosed in Patent Literature 2 (JP H4-325736 A) including an electric motor for providing torque assistance to an internal combustion engine when starting or accelerating a vehicle, a battery charging state is detected, an auxiliary torque amount (assistance amount) that can be supplied from the electric motor to the internal combustion engine is calculated based on the detected charging state, and the amount of fuel supplied to the internal combustion engine and the ratio to be borne by the electric motor are varied based on the auxiliary torque amount. Thus, electricity supply to the electric motor is stopped when the charging percentage is small, thereby preventing the battery from going flat.
Vehicles that employ a hydraulic operation mechanism for a transmission as a hydraulic vehicle operation device include a vehicle in which a transmission hydraulic pump provided in the transmission is driven by a running-drive electric motor, and a desired transmission gear ratio is achieved by controlling, with a controller, transmission hydraulic pressure supplied from this transmission hydraulic pump. With such a transmission with a transmission hydraulic pump driven by an electric motor, in order to avoid incapability to smoothly shift gears due to a delay in the rise of transmission hydraulic pressure, the transmission hydraulic pressure is always supplied to the transmission by constantly rotating the electric motor. However, the constant rotation of the electric motor is uneconomical due to needless battery consumption. To solve this problem, with a hydraulic transmission control device disclosed in Patent Literature 3 (JP H07-174218 A), an electric motor for driving a transmission hydraulic pump is stopped in a state where a shift lever is set to a parking range or a neutral range, a hand brake is pulled, and an accelerator pedal is not stepped, and meanwhile, the electric motor is actuated in a state where the shift lever is set to the parking range or the neutral range, when at least the hand brake is released or the accelerator pedal is stepped. In other words, the timing of control for turning on/off an electric-hydraulic pump is determined in accordance with the state of vehicle operation, thereby suppressing needless rotation of the electric-hydraulic pump, that is, an electric motor for driving a pump, and suppressing battery consumption. Although the battery consumption is suppressed by controlling the turning on/off of the electric-hydraulic pump when hydraulic pressure is necessary in this hydraulic vehicle operation device, control for optimizing the amount of hydraulic pressure by adjusting the number of rotations of the hydraulic pump is not taken into account.
Also, Patent Literature 4 (JP H06-107215 A) recites a vehicle in which a vehicle electric-hydraulic power-steering device using an electric-hydraulic pump is mounted as a hydraulic vehicle operation device. With this vehicle electric-hydraulic power-steering device, when a steering wheel is operated, a driving wheel is steered through a steering mechanism in accordance with the steering wheel operation. At this time, the electric-hydraulic pump operates with an electric motor, which serves as a driving source, to drive hydraulic fluid, the hydraulic fluid is supplied to a piston mechanism through a hydraulic circuit, and the steering in the steering mechanism is assisted by the piston mechanism. The operation of the electric-hydraulic pump is controlled by a pump control means based on a detection signal from a steering angle detection means, and particularly, if it is determined by a straight running determination means that the vehicle is in a straight running mode in a case where the steering angle detected by the steering angle detection means is smaller than or equal to a predetermined amount and a frequency of change in a steering state is higher than or equal to a predetermined frequency, the operation of the electric-hydraulic pump is stopped by a pump stop means provided in the pump control means. Battery consumption is suppressed by stopping the electric-hydraulic pump in a case of straight running and a certain steering angle. However, particularly with work vehicles operated at a larger steering angle, such as a tractor, the necessary amount of hydraulic pressure that should be supplied to a hydraulic circuit varies in various steering processes, and it therefore is insufficient to simply perform control for turning on/off the electric-hydraulic pump under the only conditions of straight running and curve driving.